The present invention relates to an electric rotating machine, and more specifically, to an electric rotating machine including coaxially disposed inner and outer rotors and a stator disposed between the inner and outer rotors.
Japanese Patent Application First Publication No. 11-356015 discloses an electric rotating machine including a stator having a single coil and two rotors which are different in number of magnetic poles from each other and coaxially disposed inside and outside the stator. The stator and the inner and outer rotors form a three-layered structure. The inner and outer rotors are independently driven by applying a compound current to the coil of the stator. Upon application of the compound current, the stator generates two rotating magnetic fields respectively exerted to the two rotors.
FIG. 13 illustrates a stator core useable in the stator of the three-layered electric rotating machine of the related art explained above. As illustrated in FIG. 13, stator core 100 includes a plurality of stator pieces 11. Each of stator pieces 11 has a predetermined shape to form a magnetic circuit which allows passage of magnetic flux. Stator piece 11 is formed by laminating a plurality of steel plates. Stator piece 11 radially extends and has outer yoke 15 and inner yoke 16. Stator pieces 11 are circumferentially spaced from each other with air gaps 12 between outer yokes 15 of adjacent stator pieces 11 and between inner yokes 16 thereof. Generally, in the stator for the three-layered electric rotating machine driven by the compound current, air gap 12 between adjacent stator pieces 11 is formed in order to prevent flux leakage of stator core 100 relative to the inner and outer rotors. In the case of an electric rotating machine having one rotor and a stator, stator pieces of the stator are continuously connected with each other without air gap therebetween to thereby form a magnetic path or a magnetic circuit between the rotor and the stator. Coil area 13 is formed between outer and inner yokes 15 and 16. Bolt hole 14 is disposed on the side of inner yoke 16 between adjacent stator pieces 11. Coil is inserted into coil area 13 and wound on stator piece 11. Stator core 100 with the coils are interposed between brackets disposed on opposed axial ends of stator core 100. Fastening bolts are inserted into bolt holes 14 and tightened to cause a friction force between stator core 100 and the brackets. Owing to the friction force, stator core 100 is fixedly supported between the brackets.